1. Field of the Invention
The present invention relates to a non-volatile memory device and a method for manufacturing such devices and, more particularly, to a non-volatile memory device having a dielectric film exhibiting high permitivity and superior electric properties produced according to the disclosed manufacturing method.
2. Description of the Related Art
In general, semiconductor memory devices can be divided into two main types according to the manner in which they store. The basis of this division is that volatile memory devices, such as DRAM (dynamic random access memory), must periodically restore the data and non-volatile memory devices such as SRAMs (static random access memory) and flash memories, do not need to periodically restore the data.
These two basic types of memory devices have different advantages and disadvantages that tend to make one type more suitable for a particular application. Engineers and designers typically evaluate the product needs and select the appropriate type of memory best suited for the particular application. In the case of flash memory devices, a type of non-volatile memory device, the demand is gradually increasing with the expanding market for portable electronic products. A dielectric film is used in the cell transistors of a flash memory device to insulate both a floating gate and a control gate. This dielectric film simultaneously functions as a dielectric layer in the cell capacitors of the flash memory.
A conventional ONO (oxide film/nitride film/oxide film) dielectric thin film, although commonly used as a dielectric film in flash memory devices, does not provide sufficient capacitance for operating the next generation flash memory products. In particular, it is difficult to reduce the thickness of an oxide film grown on heavily doped polysilicon using a thermal oxidation method without suffering a deterioration in the electrical properties. This deterioration is due to the high phosphorous (P) concentration in the floating gate, a high defective density, and irregularity and non-uniformity in the oxide produced by oxidizing the heavily doped polysilicon. Each of these factors lowers the effective capacitance, thereby preventing sufficient capacitance from being obtained.
Thus, a Ta2O5 thin film which may be broadly applied to DRAM products over 256M bytes may also be widely utilized as a dielectric film in flash memory devices. However, because the Ta2O5 film has an unstable stoichiometry, substitution type tantalum atoms (vacancy atoms) are generated as a result of differences in the combination ratio between tantalum (Ta) and oxygen (O) existing in the deposited thin film. In the Ta2O5 film, the substitution type tantalum atoms in an oxygen vacancy state always exist as a result of the unstable composition of the film itself. Thus, to compensate for the naturally unstable stoichiometry of Ta2O5 and prevent leakage current, a separate post-deposition oxidation process to more completely oxidize the substitution type tantalum atoms is required.
Also impurities such as, carbon (C) atoms, carbon compounds (CH4 and C2H4) and water (H2O) are created during the formation of the thin film as a result of reactions between the organometallic Ta(OC2H5) precursor to the Ta2O5 film and O2 (or N2O) gases. These impurities are, in turn, incorporated into the film, increasing leakage current generated from the floating gate of a cell transistor through the dielectric film, thereby deteriorating the dielectric properties.
For these reasons, Ta2O5 thin films are not generally applicable as the dielectric film for a cell transistor in flash memory devices.
To solve the above problem, it is an objective of the present invention to provide a method for manufacturing a non-volatile memory device that provides sufficient capacitance to meet the needs of a highly integrated memory devices.
It is another objective of the present invention to provide a non-volatile memory device having superior electric properties by using a dielectric film having high permitivity, and a method for manufacturing such a device.
It is yet another objective of the present invention to provide a method for manufacturing non-volatile memory devices in which the number of manufacturing process steps are reduced, the manufacturing cost is reduced, and the productivity is improved.
Accordingly, to achieve the above objectives, there is provided a non-volatile memory device comprising a semiconductor substrate, a gate insulating film formed on the semiconductor substrate, a floating gate formed on the gate insulating film, a dielectric film formed of a (TaO)1-x(TiO)xN on the floating gate, and a control gate formed on the dielectric film.
Also, to achieve the above objectives, there is provided a method for manufacturing a non-volatile memory device comprising the steps of providing a semiconductor substrate, forming a gate insulating film on the semiconductor substrate, forming a floating gate on the gate insulating film, forming a dielectric film by depositing (TaO)1-x(TiO)xN on the floating gate, and forming a control gate on the dielectric film.
Also, to achieve the above objectives, there is provided a method for manufacturing a non-volatile memory device comprising the steps of providing a semiconductor substrate, forming a gate insulating film on the semiconductor substrate, forming a polysilicon layer and a hemispherical grain polysilicon layer for a floating gate on the gate insulating film, nitrifying the hemispherical grain polysilicon layer, forming a dielectric film by depositing (TaO)1-x(TiO)xN on the and the nitrified hemispherical grain polysilicon layer, inducing crystallization of the dielectric film through a thermal process using an electric furnace or a rapid thermal process on the surface of the dielectric film, and forming a control gate on the dielectric film.